Process to reduce ethanol recycled to hydrogenation reactor

ABSTRACT

The present invention is directed to processes for recovering ethanol obtained from the hydrogenation of acetic acid. Acetic acid is hydrogenated in the presence of a catalyst in a hydrogenation reactor to form a crude ethanol product. The crude ethanol product is separated in one or more columns to recover ethanol. In some embodiments, less than 10 wt. % ethanol is recycled to the hydrogenation reactor.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Prov. App. No. 61/576,190,filed on Dec. 15, 2011, the entire contents and disclosures of which areincorporated herein by reference. This application is also acontinuation-in-part of U.S. application Ser. No. 13/292,914, filed onNov. 9, 2011, and U.S. application Ser. No. 13/094,588, filed on Apr.26, 2011, the entire contents and disclosures of which are incorporatedherein by reference.

FIELD OF THE INVENTION

The present invention relates generally to improving the recovery ofethanol using distillation columns and, in particular, to a process forreducing the ethanol recycled to the hydrogenation reactor.

BACKGROUND OF THE INVENTION

Ethanol for industrial use is conventionally produced from organic feedstocks, such as petroleum oil, natural gas, or coal, from feed stockintermediates, such as syngas, or from starchy materials or cellulosicmaterials, such as corn or sugar cane. Conventional methods forproducing ethanol from organic feed stocks, as well as from cellulosicmaterials, include the acid-catalyzed hydration of ethylene, methanolhomologation, direct alcohol synthesis, and Fischer-Tropsch synthesis.Instability in organic feed stock prices contributes to fluctuations inthe cost of conventionally produced ethanol, making the need foralternative sources of ethanol production all the greater when feedstock prices rise. Starchy materials, as well as cellulosic materials,are converted to ethanol by fermentation. However, fermentation istypically used for consumer production of ethanol, which is suitable forfuels or human consumption. In addition, fermentation of starchy orcellulosic materials competes with food sources and places restraints onthe amount of ethanol that can be produced for industrial use.

Ethanol production via the reduction of alkanoic acids and/or othercarbonyl group-containing compounds has been widely studied, and avariety of combinations of catalysts, supports, and operating conditionshave been mentioned in the literature. During the reduction of alkanoicacids, e.g., acetic acid, other compounds are formed with ethanol or areformed in side reactions. These impurities limit the production andrecovery of ethanol from such reaction mixtures. For example, duringhydrogenation, esters are produced that together with ethanol and/orwater form azeotropes, which are difficult to separate. In addition,when conversion is incomplete, acid remains in the crude ethanol stream,which must be removed to recover ethanol.

EP02060553 describes a process for converting hydrocarbons to ethanolinvolving converting the hydrocarbons to ethanoic acid and hydrogenatingthe ethanoic acid to ethanol. The stream from the hydrogenation reactoris separated to obtain an ethanol stream and a stream of acetic acid andethyl acetate, which is recycled to the hydrogenation reactor.

U.S. Pat. No. 7,842,844 describes a process for improving selectivityand catalyst activity and operating life for the conversion ofhydrocarbons to ethanol and optionally acetic acid in the presence of aparticulate catalyst, said conversion proceeding via a syngas generationintermediate step.

The need remains for improved processes for recovering ethanol from acrude product obtained by reducing alkanoic acids, such as acetic acid,and/or other carbonyl group-containing compounds.

SUMMARY OF THE INVENTION

In a first embodiment, the present invention is directed to a processfor producing ethanol, comprising hydrogenating acetic acid and/or anester thereof in a reactor in the presence of a catalyst to form a crudeethanol stream, separating a portion of the crude ethanol stream in afirst distillation column to yield a first distillate comprisingacetaldehyde, ethyl acetate, and ethanol, and a first residue comprisingethanol and ethyl acetate, separating a portion of the first residue ina second distillation column to yield a second residue comprising aceticacid and a second distillate comprising ethanol, and ethyl acetate, andrecovering ethanol from the second distillate. In some embodiments, thefirst residue may comprise low amounts of acetic acid. In oneembodiment, the process comprises separating at least a portion of thesecond distillate in a third distillation column to yield a thirddistillate comprising ethyl acetate and a third residue comprisingethanol. The first distillate is returned to the reactor and less than10% of the ethanol, e.g., less than 5%, from the crude ethanol stream isreturned to the reactor. In one embodiment, the first distillate isfurther separated to yield an ethanol stream and a raffinate streamcomprising ethyl acetate and less than 2 wt. % ethanol. In furtherembodiments, the ethanol has a ¹⁴C:¹²C ratio of the acetic acid from 0.5to 1 of the ¹⁴C:¹²C ratio for living organisms. A total diameter for thefirst distillation column, the second distillation column and the thirddistillation column may be from 5 to 40 meters and further wherein aratio of total column diameter for the first distillation column, thesecond distillation column and the third distillation column to tons ofethanol produced per hour is from 1:2 to 1:30.

In a second embodiment, the present invention is directed to a processfor producing ethanol, comprising hydrogenating acetic acid and/or anester thereof in a reactor in the presence of a catalyst to form a crudeethanol stream, separating a portion of the crude ethanol stream in afirst distillation column to yield a first distillate comprisingacetaldehyde, ethyl acetate and ethanol, wherein the first distillatehas less than 10% of the ethanol, e.g., less than 5%, from the crudeethanol stream, and a first residue comprising ethanol, acetic acid,ethyl acetate and water, wherein the first residue has at least 90% ofthe ethanol, e.g., at least 95%, from the crude ethanol stream,separating a portion of the first residue in a second distillationcolumn to yield a second residue comprising acetic acid and a seconddistillate comprising ethanol and ethyl acetate, and separating at leasta portion of the second distillate in a third distillation column toyield a third distillate comprising ethyl acetate and a third residuecomprising ethanol. The first distillate may be returned to the reactor.

In a third embodiment, the present invention is directed to a processfor producing ethanol, comprising hydrogenating acetic acid and/or anester thereof in a reactor in the presence of a catalyst to form a crudeethanol stream, separating a portion of the crude ethanol stream in afirst distillation column to yield a first distillate comprisingacetaldehyde, ethyl acetate and ethanol, and a first residue comprisingethanol and acetic acid, separating a portion of the first distillate toyield an ethanol stream and a raffinate stream comprising ethyl acetate,wherein the raffinate is returned to the reactor, separating a portionof the first residue in a second distillation column to yield a secondresidue comprising acetic acid and a second distillate comprisingethanol, and recovering ethanol from the second residue. In oneembodiment, the process may comprise separating at least a portion ofthe second distillate in a third distillation column to yield a thirddistillate comprising ethyl acetate and a third residue comprisingethanol.

In a fourth embodiment, the present invention is directed to a processfor producing ethanol, comprising hydrogenating acetic acid and/or anester thereof in a reactor in the presence of a catalyst to form a crudeethanol stream, separating a portion of the crude ethanol stream in afirst distillation column to yield a first distillate comprisingacetaldehyde and ethyl acetate, and a first residue comprising ethanol,acetic acid and water, converting a portion of the first residue into apartial vapor feed having less than 30 mol. %, preferably less than 25mol. %, of the contents in the vapor phase, separating a portion of thepartial vapor feed in a second distillation column to yield a secondresidue comprising acetic acid and an second distillate comprisingethanol, and recovering ethanol from the second distillate. The firstresidue may be converted to the partial vapor feed using a secondaryreactor or secondary vaporizer. In one embodiment, the secondary reactoris a vapor phase esterification reactor.

In a fifth embodiment, the present invention is directed to a processfor producing ethanol, comprising hydrogenating acetic acid and/or anester thereof in a reactor in the presence of a catalyst to form a crudeethanol stream, separating a portion of the crude ethanol stream in afirst distillation column to yield a first distillate comprisingacetaldehyde, ethyl acetate and ethanol, and a first residue comprisingethanol, acetic acid, ethyl acetate and water, converting a portion ofthe first residue into a partial vapor feed having less than 30 mol. %,preferably less than 25 mol. %, of the contents in the vapor phase,separating a portion of the partial vapor feed in a second distillationcolumn to yield a second residue comprising acetic acid and a seconddistillate comprising ethanol, and ethyl acetate, and recovering ethanolfrom the second distillate. In one embodiment, the process comprisesseparating at least a portion of the second distillate in a thirddistillation column to yield a third distillate comprising ethyl acetateand a third residue comprising ethanol. The first distillate is returnedto the reactor and less than 10% of the ethanol, e.g., less than 5%,from the crude ethanol stream is returned to the reactor. In oneembodiment, the first distillate is further separated to yield anethanol stream and a raffinate stream comprising ethyl acetate and lessthan 2 wt. % ethanol.

In a sixth embodiment, the present invention is directed to a processfor producing ethanol, comprising providing a crude ethanol stream,separating a portion of the crude ethanol stream in a first distillationcolumn to yield a first distillate comprising acetaldehyde, ethylacetate, and ethanol, and a first residue comprising ethanol and ethylacetate, separating a portion of the first residue in a seconddistillation column to yield a second residue comprising acetic acid anda second distillate comprising ethanol, and ethyl acetate, andrecovering ethanol from the second distillate. In some embodiments, thefirst residue may comprise low amounts of acetic acid. In oneembodiment, the process comprises separating at least a portion of thesecond distillate in a third distillation column to yield a thirddistillate comprising ethyl acetate and a third residue comprisingethanol. The first distillate is returned to the reactor and less than10% of the ethanol, e.g., less than 5%, from the crude ethanol stream isreturned to the reactor. In one embodiment, the first distillate isfurther separated to yield an ethanol stream and a raffinate streamcomprising ethyl acetate and less than 2 wt. % ethanol. In furtherembodiments, the ethanol has a ¹⁴C:¹²C ratio of the acetic acid from 0.5to 1 of the ¹⁴C:¹²C ratio for living organisms. A total diameter for thefirst distillation column, the second distillation column and the thirddistillation column may be from 5 to 40 meters and further wherein aratio of total column diameter for the first distillation column, thesecond distillation column and the third distillation column to tons ofethanol produced per hour is from 1:2 to 1:30. The process may furthercomprise converting a portion of the first residue into a partial vaporfeed having less than 30 mol. %, preferably less than 25 mol. %, of thecontents in the vapor phase; separating a portion of the partial vaporfeed in a second distillation column to yield a second residuecomprising acetic acid and a second distillate comprising ethanol; andrecovering ethanol from the second distillate.

BRIEF DESCRIPTION OF DRAWINGS

The invention may be more completely understood in consideration of thefollowing detailed description of various embodiments of the inventionin connection with the accompanying drawings, wherein like numeralsdesignate similar parts.

FIG. 1 is a schematic diagram of an ethanol production system withmultiple distillation columns to recover ethanol including an acidcolumn and water separator in accordance with one embodiment of thepresent invention.

FIG. 2 is a schematic diagram of an ethanol production system withmultiple distillation columns having a process for vaporizing at least aportion of the feed to the second column in accordance with oneembodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to processes for recovering ethanolproduced by hydrogenating acetic acid in the presence of a catalyst. Thehydrogenation reaction produces a crude ethanol stream that comprisesethanol, water, ethyl acetate, acetaldehyde, and other impurities. Theprocesses of the present invention involve separating the crude ethanolstream in a first column into a residue stream comprising ethanol,water, ethyl acetate and acetic acid and a distillate stream comprisingacetaldehyde and ethyl acetate. The first column primarily removes lightorganics in the distillate and returns those organics for subsequenthydrogenation. Even though a majority of the ethanol is removed in theresidue stream to yield an ethanol product, some of the ethanol iswithdrawn with the distillate and the first distillate is recycled tothe reactor.

In one embodiment, it is preferred to return to the reactor less than10% of the ethanol from the crude ethanol stream, e.g., less than 5% orless than 1%. In terms of ranges, the amount of returned ethanol is from0.01 to 10% of the ethanol in the crude ethanol stream, e.g. from 0.1 to5% or from 0.2 to 1%. In one embodiment, to reduce the amount of ethanolrecycled, the present invention operates the first column to remove moreethanol in the residue, either using an extractive agent and/orpressure. In another embodiment, the distillate of the first residue maybe extracted to withdraw ethanol and reduce the ethanol recycled to thehydrogenation reactor. Without reducing the ethanol recycled, moreethanol would pass through the hydrogenation reactor, causing anundesirable loss of ethanol productivity.

Advantageously, this separation approach results in reducing energyrequirements to recover ethanol, in particular anhydrous ethanol forfuel grade ethanol, from the crude ethanol stream.

In recovering ethanol, the processes of the present invention use one ormore distillation columns. In preferred embodiments, the residue streamin the initial column, e.g., first column, comprises more ethanol thanthe distillate stream in the initial column. In some embodiments, theresidue stream comprises a substantial portion of the ethanol, water andacetic acid from the crude ethanol stream. In terms of ranges, theresidue stream may comprise from 50% to 99.9% of the ethanol from thecrude ethanol product, e.g. 70% to 99.9%, or 90 to 99.5%. Preferably,the amount of ethanol from the crude ethanol product recovered in theresidue may be greater than 97.5%, e.g. greater than 99%.

The residue stream comprising ethanol, ethyl acetate, water and aceticacid may be further separated to recover ethanol. Because thesecompounds may not be in equilibrium, additional ethyl acetate may beproduced through esterification of ethanol and acetic acid. In onepreferred embodiment, the water and acetic acid may be removed asanother residue stream in a separate distillation column. In addition,the water carried over in the separate distillation column may beremoved with a water separator that is selected from the groupconsisting of an adsorption unit, membrane, extractive columndistillation, molecular sieves, and combinations thereof.

Although ethyl acetate is partially withdrawn into the first distillate,a higher ethyl acetate concentration in the first residue leads toincreased ethanol concentration in the first residue and decreasedethanol concentrations in the first distillate. Thus, overall ethanolrecovery may be increased. Depending on the ethyl acetate concentrationin the residue and whether there is in situ esterification in theresidue or an esterification reactor, it may be necessary to furtherseparate the ethyl acetate and ethanol in a separate column. Preferably,this separate column is located after the water has been removed using adistillation column and/or water separator. Generally, a separate columnmay be necessary when the residue comprises at least 50 wppm ethylacetate or there is in situ esterification. When the ethyl acetate isless than 50 wppm, it may not be necessary to use separate column toseparate ethyl acetate and ethanol.

Ethyl acetate may be separated from ethanol in a separate column nearthe end of the purification process. In removing ethyl acetate,additional light organics may also be removed, thus improving thequality of the ethanol product by decreasing impurities. Preferably,water and/or acetic acid may be removed prior to the ethylacetate/ethanol separation. In one embodiment, after the ethyl acetateis separated from ethanol, the ethyl acetate is returned to the initialcolumn and fed near the top of that column. This allows for any ethanolremoved with the ethyl acetate to be recovered and further reduces theamount of ethanol being recycled to the reactor. In some embodiments, itis preferably to recycle ethanol within the separation zone but todecrease the amount of ethanol recycled to the reactor. Decreasing theamount of ethanol recycled to the reactor may reduce reactor capital andimprove efficiency in recovering ethanol. Preferably, the ethyl acetateis removed in the distillate of the first column and returned to thereactor with the acetaldehyde.

In preferred embodiments, the residue stream of the first columncomprises a substantial portion of the water and the acetic acid fromthe crude ethanol stream. The residue stream may comprise at least 80%of the water from the crude ethanol stream, and more preferably at least90%. In terms of ranges, the residue stream preferably comprises from80% to 100% of the water from the crude ethanol stream, and morepreferably from 90% to 99.4%. The residue stream may comprise at least85% of the acetic acid from the crude ethanol stream, e.g., at least 90%and more preferably about 100%. In terms of ranges, the residue streampreferably comprises from 85% to 100% of the acetic acid from the crudeethanol stream, and more preferably from 90% to 100%. In one embodiment,substantially all of the acetic acid is recovered in the residue stream.

In one embodiment, each of the columns is sized to be capital andeconomically feasible for the rate of ethanol production. The totaldiameter for the columns used to separate the crude ethanol stream maybe from 5 to 40 meters, e.g., from 10 to 30 meters or from 12 to 20meters. Each column may have a varying size. In one embodiment, theratio of column diameter in meters for all the distillation columns totons of ethanol produced per hour is from 1:2 to 1:30, e.g., from 1:3 to1:20 or from 1:4 to 1:10. This would allow the process to achieveproduction rates of 25 to 250 tons of ethanol per hour.

The distillate from the initial column comprises light organics, such asacetaldehyde, diethyl acetal, acetone and ethyl acetate. In addition,minor amounts of ethanol and water may be present in the distillate.Removing these light organic components from the crude ethanol stream inthe initial column provides an efficient means for removing acetaldehydeand ethyl acetate. In addition, acetaldehyde, diethyl acetal and acetoneare not carried over with the ethanol when multiple columns are used,thus reducing the formation of byproducts from acetaldehyde, diethylacetal, and acetone. In particular, acetaldehyde and/or ethyl acetatemay be returned to the reactor, and converted to additional ethanol. Inanother embodiment, a purge may remove these light organics from thesystem.

The residue from the initial column comprises ethyl acetate. Althoughethyl acetate is also partially withdrawn into the first distillate, ahigher ethyl acetate concentration in the first residue leads toincreased ethanol concentration in the first residue and decreaseethanol concentrations in the first distillate. Thus overall ethanolrecovery may be increased. Ethyl acetate may be separated from ethanolin a separate column near the end of the purification process. Inremoving ethyl acetate, additional light organics may also be removedand thus improve the quality of the ethanol product by decreasingimpurities. Preferably, water and/or acetic acid may be removed prior tothe ethyl acetate/ethanol separation.

In one embodiment, after the ethyl acetate is separated from ethanol,the ethyl acetate is returned to the initial column and fed near the topof that column. This allows for any ethanol removed with the ethylacetate to be recovered and further reduces the amount of ethanol beingrecycled to the reactor. Decreasing the amount of ethanol recycled tothe reactor may reduce reactor capital and improve efficiency inrecovering ethanol. Preferably, the ethyl acetate is removed in thedistillate of the first column and returned to the reactor with theacetaldehyde.

The process of the present invention may be used with any hydrogenationprocess for producing ethanol. The materials, catalysts, reactionconditions, and separation processes that may be used in thehydrogenation of acetic acid are described further below.

The raw materials, acetic acid and hydrogen, used in connection with theprocess of this invention may be derived from any suitable sourceincluding natural gas, petroleum, coal, biomass, and so forth. Asexamples, acetic acid may be produced via methanol carbonylation,acetaldehyde oxidation, ethane oxidation, oxidative fermentation, andanaerobic fermentation. Methanol carbonylation processes suitable forproduction of acetic acid are described in U.S. Pat. Nos. 7,208,624;7,115,772; 7,005,541; 6,657,078; 6,627,770; 6,143,930; 5,599,976;5,144,068; 5,026,908; 5,001,259; and 4,994,608, the entire disclosuresof which are incorporated herein by reference. Optionally, theproduction of ethanol may be integrated with such methanol carbonylationprocesses.

As petroleum and natural gas prices fluctuate becoming either more orless expensive, methods for producing acetic acid and intermediates suchas methanol and carbon monoxide from other carbon sources have drawnincreasing interest. In particular, when petroleum is relativelyexpensive, it may become advantageous to produce acetic acid fromsynthesis gas (“syngas”) that is derived from other available carbonsources. U.S. Pat. No. 6,232,352, the entirety of which is incorporatedherein by reference, for example, teaches a method of retrofitting amethanol plant for the manufacture of acetic acid. By retrofitting amethanol plant, the large capital costs associated with CO generationfor a new acetic acid plant are significantly reduced or largelyeliminated. All or part of the syngas is diverted from the methanolsynthesis loop and supplied to a separator unit to recover CO, which isthen used to produce acetic acid. In a similar manner, hydrogen for thehydrogenation step may be supplied from syngas.

In some embodiments, some or all of the raw materials for theabove-described acetic acid hydrogenation process may be derivedpartially or entirely from syngas. For example, the acetic acid may beformed from methanol and carbon monoxide, both of which may be derivedfrom syngas. The syngas may be formed by partial oxidation reforming orsteam reforming, and the carbon monoxide may be separated from syngas.Similarly, hydrogen that is used in the step of hydrogenating the aceticacid to form the crude ethanol stream may be separated from syngas. Thesyngas, in turn, may be derived from a variety of carbon sources. Thecarbon source, for example, may be selected from the group consisting ofnatural gas, oil, petroleum, coal, biomass, and combinations thereofSyngas or hydrogen may also be obtained from bio-derived methane gas,such as bio-derived methane gas produced by landfills or agriculturalwaste.

Biomass-derived syngas has a detectable ¹⁴C isotope content as comparedto fossil fuels such as coal or natural gas. An equilibrium forms in theEarth's atmosphere between constant new formation and constantdegradation, and so the proportion of the ¹⁴C nuclei in the carbon inthe atmosphere on Earth is constant over long periods. The samedistribution ratio n¹⁴C:n¹²C ratio is established in living organisms asis present in the surrounding atmosphere, which stops at death and ¹⁴Cdecomposes at a half life of about 6000 years. Methanol, acetic acidand/or ethanol formed from biomass-derived syngas would be expected tohave a ¹⁴C content that is substantially similar to living organisms.For example, the ¹⁴C:¹²C ratio of the methanol, acetic acid and/orethanol may be from one half to about 1 of the ¹⁴C:¹²C ratio for livingorganisms. In other embodiments, the syngas, methanol, acetic acidand/or ethanol described herein are derived wholly from fossil fuels,i.e. carbon sources produced over 60,000 years ago, may have nodetectable ¹⁴C content.

In another embodiment, the acetic acid used in the hydrogenation stepmay be formed from the fermentation of biomass. The fermentation processpreferably utilizes an acetogenic process or a homoacetogenicmicroorganism to ferment sugars to acetic acid producing little, if any,carbon dioxide as a by-product. The carbon efficiency for thefermentation process preferably is greater than 70%, greater than 80% orgreater than 90% as compared to conventional yeast processing, whichtypically has a carbon efficiency of about 67%. Optionally, themicroorganism employed in the fermentation process is of a genusselected from the group consisting of Clostridium, Lactobacillus,Moorella, Thermoanaerobacter, Propionibacterium, Propionispera,Anaerobiospirillum, and Bacteriodes, and in particular, species selectedfrom the group consisting of Clostridium formicoaceticum, Clostridiumbutyricum, Moorella thermoacetica, Thermoanaerobacter kivui,Lactobacillus delbrukii, Propionibacterium acidipropionici,Propionispera arboris, Anaerobiospirillum succinicproducens, Bacteriodesamylophilus and Bacteriodes ruminicola. Optionally, in this process, allor a portion of the unfermented residue from the biomass, e.g., lignans,may be gasified to form hydrogen that may be used in the hydrogenationstep of the present invention. Exemplary fermentation processes forforming acetic acid are disclosed in U.S. Pat. No. 6,509,180, and U.S.Pub. Nos. 2008/0193989 and 2009/0281354, the entireties of which areincorporated herein by reference.

Examples of biomass include, but are not limited to, agriculturalwastes, forest products, grasses, and other cellulosic material, timberharvesting residues, softwood chips, hardwood chips, tree branches, treestumps, leaves, bark, sawdust, off-spec paper pulp, corn, corn stover,wheat straw, rice straw, sugarcane bagasse, switchgrass, miscanthus,animal manure, municipal garbage, municipal sewage, commercial waste,grape pumice, almond shells, pecan shells, coconut shells, coffeegrounds, grass pellets, hay pellets, wood pellets, cardboard, paper,plastic, and cloth. Another biomass source is black liquor, which is anaqueous solution of lignin residues, hemicellulose, and inorganicchemicals.

U.S. Pat. No. RE 35,377, also incorporated herein by reference, providesa method for the production of methanol by converting carbonaceousmaterials such as oil, coal, natural gas and biomass materials. Theprocess includes hydrogasification of solid and/or liquid carbonaceousmaterials to obtain a process gas which is steam pyrolized withadditional natural gas to form syngas. The syngas is converted tomethanol which may be carbonylated to acetic acid. The method likewiseproduces hydrogen which may be used in connection with this invention asnoted above. U.S. Pat. No. 5,821,111, which discloses a process forconverting waste biomass through gasification into synthesis gas, andU.S. Pat. No. 6,685,754, which discloses a method for the production ofa hydrogen-containing gas composition, such as a syngas includinghydrogen and carbon monoxide, are incorporated herein by reference intheir entireties.

Acetic acid fed to the hydrogenation reactor may also comprise othercarboxylic acids and anhydrides, as well as acetaldehyde and acetone.Preferably, a suitable acetic acid feed stream comprises one or more ofthe compounds selected from the group consisting of acetic acid, aceticanhydride, acetaldehyde, ethyl acetate, and mixtures thereof. Theseother compounds may also be hydrogenated in the processes of the presentinvention. In some embodiments, the presence of carboxylic acids, suchas propanoic acid or its aldehyde, may be beneficial in producingpropanol. Water may also be present in the acetic acid feed.

Alternatively, acetic acid in vapor form may be taken directly as crudeproduct from the flash vessel of a methanol carbonylation unit of theclass described in U.S. Pat. No. 6,657,078, the entirety of which isincorporated herein by reference. The crude vapor product, for example,may be fed directly to the ethanol synthesis reaction zones of thepresent invention without the need for condensing the acetic acid andlight ends or removing water, saving overall processing costs.

The acetic acid may be vaporized at the reaction temperature, followingwhich the vaporized acetic acid may be fed along with hydrogen in anundiluted state or diluted with a relatively inert carrier gas, such asnitrogen, argon, helium, carbon dioxide and the like. For reactions runin the vapor phase, the temperature should be controlled in the systemsuch that it does not fall below the dew point of acetic acid. In oneembodiment, the acetic acid may be vaporized at the boiling point ofacetic acid at the particular pressure, and then the vaporized aceticacid may be further heated to the reactor inlet temperature. In anotherembodiment, the acetic acid is mixed with other gases before vaporizing,followed by heating the mixed vapors up to the reactor inlettemperature. Preferably, the acetic acid is transferred to the vaporstate by passing hydrogen and/or recycle gas through the acetic acid ata temperature at or below 125° C., followed by heating of the combinedgaseous stream to the reactor inlet temperature.

Some embodiments of the process of hydrogenating acetic acid to formethanol may include a variety of configurations using a fixed bedreactor or a fluidized bed reactor. In many embodiments of the presentinvention, an “adiabatic” reactor can be used; that is, there is littleor no need for internal plumbing through the reaction zone to add orremove heat. In other embodiments, a radial flow reactor or reactors maybe employed, or a series of reactors may be employed with or withoutheat exchange, quenching, or introduction of additional feed material.Alternatively, a shell and tube reactor provided with a heat transfermedium may be used. In many cases, the reaction zone may be housed in asingle vessel or in a series of vessels with heat exchangerstherebetween.

In preferred embodiments, the catalyst is employed in a fixed bedreactor, e.g., in the shape of a pipe or tube, where the reactants,typically in the vapor form, are passed over or through the catalyst.Other reactors, such as fluid or ebullient bed reactors, can beemployed. In some instances, the hydrogenation catalysts may be used inconjunction with an inert material to regulate the pressure drop of thereactant stream through the catalyst bed and the contact time of thereactant compounds with the catalyst particles.

The hydrogenation reaction may be carried out in either the liquid phaseor vapor phase. Preferably, the reaction is carried out in the vaporphase under the following conditions. The reaction temperature may rangefrom 125° C. to 350° C., e.g., from 200° C. to 325° C., from 225° C. to300° C., or from 250° C. to 300° C. The pressure may range from 10 kPato 3000 kPa, e.g., from 50 kPa to 2300 kPa, or from 100 kPa to 2100 kPa.The reactants may be fed to the reactor at a gas hourly space velocity(GHSV) from 50 hr⁻¹ to 50,000 hr⁻¹, e.g., from 500 hr⁻¹ to 30,000 hr⁻¹,from 1000 hr⁻¹ to 10,000 hr⁻¹, or from 1000 hr⁻¹ to 6500 hr⁻¹.

Although the reaction consumes two moles of hydrogen per mole of aceticacid to produce one mole of ethanol, the actual molar ratio of hydrogento acetic acid in the feed stream may vary from about 100:1 to 1:100,e.g., from 50:1 to 1:50, from 20:1 to 1:2, or from 18:1 to 2:1.

Contact or residence time can also vary widely, depending upon suchvariables as amount of acetic acid, catalyst, reactor, temperature, andpressure. Typical contact times range from a fraction of a second tomore than several hours when a catalyst system other than a fixed bed isused, with preferred contact times, at least for vapor phase reactions,from 0.1 to 100 seconds.

The hydrogenation of acetic acid to form ethanol is preferably conductedin the presence of a hydrogenation catalyst. Exemplary catalysts arefurther described in U.S. Pat. Nos. 7,608,744 and 7,863,489, and U.S.Pub. Nos. 2010/0121114 and 2010/0197985, the entireties of which areincorporated herein by reference. In another embodiment, the catalystcomprises a Co/Mo/S catalyst of the type described in U.S. Pub. No.2009/0069609, the entirety of which is incorporated herein by reference.In some embodiments the catalyst may be a bulk catalyst.

In one embodiment, the catalyst comprises a first metal selected fromthe group consisting of copper, iron, cobalt, nickel, ruthenium,rhodium, palladium, osmium, iridium, platinum, titanium, zinc, chromium,rhenium, molybdenum, and tungsten. Preferably, the first metal isselected from the group consisting of platinum, palladium, cobalt,nickel, and ruthenium.

As indicated above, in some embodiments, the catalyst further comprisesa second metal, which typically would function as a promoter. Ifpresent, the second metal preferably is selected from the groupconsisting of copper, molybdenum, tin, chromium, iron, cobalt, vanadium,tungsten, palladium, platinum, lanthanum, cerium, manganese, ruthenium,rhenium, gold, and nickel. More preferably, the second metal is selectedfrom the group consisting of copper, tin, cobalt, rhenium, and nickel.

In certain embodiments where the catalyst includes two or more metals,e.g., a first metal and a second metal, the first metal is present inthe catalyst in an amount from 0.1 to 10 wt. %, e.g., from 0.1 to 5 wt.%, or from 0.1 to 3 wt. %. The second metal preferably is present in anamount from 0.1 to 20 wt. %, e.g., from 0.1 to 10 wt. %, or from 0.1 to7.5 wt. %.

Preferred metal combinations for exemplary catalyst compositions includeplatinum/tin, platinum/ruthenium, platinum/rhenium, palladium/ruthenium,palladium/rhenium, cobalt/palladium, cobalt/platinum, cobalt/chromium,cobalt/ruthenium, cobalt/tin, silver/palladium, copper/palladium,copper/zinc, nickel/palladium, gold/palladium, ruthenium/rhenium, orruthenium/iron.

The catalyst may also comprise a third metal selected from any of themetals listed above in connection with the first or second metal, solong as the third metal is different from the first and second metals.In preferred aspects, the third metal is selected from the groupconsisting of cobalt, palladium, ruthenium, copper, zinc, platinum, tin,and rhenium. When present, the total weight of the third metalpreferably is from 0.05 to 20 wt. %, e.g., from 0.1 to 10 wt. %, or from0.1 to 7.5 wt. %. In one embodiment, the catalyst may comprise platinum,tin and cobalt.

In addition to one or more metals, in some embodiments of the presentinvention the catalysts further comprise a support or a modifiedsupport. As used herein, the term “modified support” refers to a supportthat includes a support material and a support modifier, which adjuststhe acidity of the support material. The total weight of the support ormodified support, based on the total weight of the catalyst, preferablyis from 75 to 99.9 wt. %, e.g., from 78 to 97 wt. %, or from 80 to 97.5wt. %. Preferred supports include silicaceous supports, such as silica,silica/alumina, a Group IIA silicate such as calcium metasilicate,pyrogenic silica, high purity silica, and mixtures thereof Othersupports may include, but are not limited to, iron oxide, alumina,titania, zirconia, magnesium oxide, carbon, graphite, high surface areagraphitized carbon, activated carbons, and mixtures thereof.

The support may be a modified support and the support modifier ispresent in an amount from 0.1 to 50 wt. %, e.g., from 0.2 to 25 wt. %,from 1 to 20 wt. %, or from 3 to 15 wt. %, based on the total weight ofthe catalyst. In some embodiments, the support modifier may be an acidicmodifier that increases the acidity of the catalyst. Suitable acidicsupport modifiers may be selected from the group consisting of: oxidesof Group IVB metals, oxides of Group VB metals, oxides of Group VIBmetals, oxides of Group VIIB metals, oxides of Group VIIIB metals,aluminum oxides, and mixtures thereof Acidic support modifiers includethose selected from the group consisting of TiO₂, ZrO₂, Nb₂O₅, Ta₂O₅,Al₂O₃, B₂O₃, P₂O₅, Sb₂O₃, WO₃, MoO₃, Fe₂O₃, Cr₂O₃, V₂O₅, MnO₂, CuO,CO₂O₃, and Bi₂O₃. Preferred support modifiers include oxides oftungsten, molybdenum, and vanadium.

In another embodiment, the support modifier may be a basic modifier thathas a low volatility or no volatility. Such basic modifiers, forexample, may be selected from the group consisting of: (i) alkalineearth metal oxides, (ii) alkali metal oxides, (iii) alkaline earth metalmetasilicates, (iv) alkali metal metasilicates, (v) Group IIB metaloxides, (vi) Group IIB metal metasilicates, (vii) Group IIIB metaloxides, (viii) Group IIIB metal metasilicates, and mixtures thereof. Thebasic support modifier may be selected from the group consisting ofoxides and metasilicates of any of sodium, potassium, magnesium,calcium, scandium, yttrium, and zinc, as well as mixtures of any of theforegoing. In one embodiment, the basic support modifier is a calciumsilicate, such as calcium metasilicate (CaSiO₃). The calciummetasilicate may be crystalline or amorphous.

Catalysts on a modified support may include one or more metals from thegroup of platinum, palladium, cobalt, tin, or rhenium on a silicasupport modified by one or more modifiers from the group of calciummetasilicate, oxides of tungsten, molybdenum, and vanadium.

The catalyst compositions suitable for use with the present inventionpreferably are formed through metal impregnation of the modifiedsupport, although other processes such as chemical vapor deposition mayalso be employed. Such impregnation techniques are described in U.S.Pat. Nos. 7,608,744 and 7,863,489 and U.S. Pub. No. 2010/0197485referred to above, the entireties of which are incorporated herein byreference.

After the washing, drying and calcining of the catalyst is completed,the catalyst may be reduced in order to activate the catalyst. Reductionis carried out in the presence of a reducing gas, preferably hydrogen.The reducing gas is continuously passed over the catalyst at an initialambient temperature that is increased up to 400° C. In one embodiment,the reduction is preferably carried out after the catalyst has beenloaded into the reaction vessel where the hydrogenation will be carriedout.

In particular, the hydrogenation of acetic acid may achieve favorableconversion of acetic acid and favorable selectivity and productivity toethanol. For purposes of the present invention, the term “conversion”refers to the amount of acetic acid in the feed that is converted to acompound other than acetic acid. Conversion is expressed as a percentagebased on acetic acid in the feed. The conversion may be at least 40%,e.g., at least 50%, at least 60%, at least 70% or at least 80%. Althoughcatalysts that have high conversions are desirable, such as at least 80%or at least 90%, in some embodiments a low conversion may be acceptableat high selectivity for ethanol.

Selectivity is expressed as a mole percent based on converted aceticacid. It should be understood that each compound converted from aceticacid has an independent selectivity and that selectivity is independentfrom conversion. For example, if 60 mole % of the converted acetic acidis converted to ethanol, we refer to the ethanol selectivity as 60%.Preferably, the catalyst selectivity to ethanol is at least 60%, e.g.,at least 70%, or at least 80%. Preferred embodiments of thehydrogenation process also have low selectivity to undesirable products,such as methane, ethane, and carbon dioxide. The selectivity to theseundesirable products preferably is less than 4%, e.g., less than 2% orless than 1%.

The term “productivity,” as used herein, refers to the grams of aspecified product, e.g., ethanol, formed during the hydrogenation basedon the kilograms of catalyst used per hour. The productivity may rangefrom 100 to 3,000 grams of ethanol per kilogram of catalyst per hour.

In various embodiments of the present invention, the crude ethanolstream produced by the hydrogenation process, before any subsequentprocessing, such as purification and separation, will typically compriseacetic acid, ethanol and water. Exemplary compositional ranges for thecrude ethanol stream are provided in Table 1, excluding hydrogen. The“others” identified in Table 1 may include, for example, esters, ethers,aldehydes, ketones, alkanes, and carbon dioxide.

TABLE 1 CRUDE ETHANOL STREAM COMPOSITIONS Conc. Conc. Conc. Conc.Component (wt. %) (wt. %) (wt. %) (wt. %) Ethanol 5 to 72 15 to 72  15to 70 25 to 65 Acetic Acid 0 to 90 0 to 50  0 to 35  0 to 15 Water 5 to40 5 to 30 10 to 30 10 to 26 Ethyl Acetate 0 to 30 1 to 25  3 to 20  5to 18 Acetaldehyde 0 to 10 0 to 3  0.1 to 3   0.2 to 2   Others 0.1 to10   0.1 to 6   0.1 to 4   —

In one embodiment, the crude ethanol stream of Table 1 may have lowconcentrations of acetic acid with higher conversion, and the aceticacid concentration may range from 0.01 wt. % to 20 wt. %, e.g., 0.05 wt.% to 15 wt. %, from 0.1 wt. % to 10 wt. % or from 1 wt. % to 5 wt. %. Inembodiments having lower amounts of acetic acid, the conversion ofacetic acid is preferably greater than 75%, e.g., greater than 85% orgreater than 90%. In addition, the selectivity to ethanol may also bepreferably high, and is preferably greater than 75%, e.g., greater than85% or greater than 90%.

Exemplary ethanol recovery systems in accordance with embodiments of thepresent invention are shown in FIGS. 1-2. Each hydrogenation system 100provides a suitable hydrogenation reactor and a process for separatingethanol from the crude reaction mixture according to an embodiment ofthe invention. System 100 comprises reaction zone 101 and separationzone 102. Further modifications and additional components to reactionzone 101 and separation zone 102 are described below. In FIG. 1 there isshown an optional extractor 120 and an esterification unit 150. In FIG.2, there is shown a secondary reactor 160 and secondary vaporizer 161for converting a portion of the first residue to the vapor phase.

As shown in FIGS. 1 and 2, the feed to reactor 103 comprises freshacetic acid. Hydrogen and acetic acid are fed to vaporizer 104 via lines105 and 106, respectively, to create a vapor feed stream in line 107that is directed to reactor 103. In one embodiment, lines 105 and 106may be combined and jointly fed to the vaporizer 104. The temperature ofthe vapor feed stream in line 107 is preferably from 100° C. to 350° C.,e.g., from 120° C. to 310° C. or from 150° C. to 300° C. Any feed thatis not vaporized is removed from vaporizer 104, via blowdown 108. Inaddition, although line 107 is shown as being directed to the top ofreactor 103, line 107 may be directed to the side, upper portion, orbottom of reactor 103.

Reactor 103 contains the catalyst that is used in the hydrogenation ofthe carboxylic acid, preferably acetic acid. In one embodiment, one ormore guard beds (not shown) may be used upstream of the reactor,optionally upstream of vaporizer 104, to protect the catalyst frompoisons or undesirable impurities contained in the feed orreturn/recycle streams. Such guard beds may be employed in the vapor orliquid streams. Suitable guard bed materials may include, for example,carbon, silica, alumina, ceramic, or resins. In one aspect, the guardbed media is functionalized, e.g., silver functionalized, to trapparticular species such as sulfur or halogens. During the hydrogenationprocess, a crude ethanol stream is withdrawn, preferably continuously,from reactor 103 via line 109.

The crude ethanol stream may be condensed and fed to a separator 110,which, in turn, forms a vapor stream 112 and a liquid stream 113. Insome embodiments, separator 110 may comprise a flasher or a knockoutpot. The separator 110 may operate at a temperature from 20° C. to 350°C., e.g., from 30° C. to 325° C. or from 60° C. to 250° C. The pressureof separator 110 may be from 100 kPa to 3000 kPa, e.g., from 125 kPa to2500 kPa or from 150 kPa to 2200 kPa. Optionally, the crude ethanolstream in line 109 may pass through one or more membranes to separatehydrogen and/or other non-condensable gases.

Vapor stream 112 exiting separator 110 may comprise hydrogen andhydrocarbons, and may be purged and/or returned to reaction zone 101. Asshown, vapor stream 112 is combined with the hydrogen feed 105 andco-fed to vaporizer 104. In some embodiments, the returned vapor stream112 may be compressed before being combined with hydrogen feed 105.

Liquid stream 113 from separator 110 is withdrawn and directed as a feedcomposition to the side of first distillation column 115, also referredto as a “light ends column.” Liquid stream 113 may be heated fromambient temperature to a temperature of up to 70° C., e.g., up to 50°C., or up to 40° C. The additional energy required to pre-heat liquidstream 113 above 70° C. does not achieve the desired energy efficiencyin first column 115 with respect to reboiler duties. In anotherembodiment, liquid stream 113 is not separately preheated, but iswithdrawn from separator 110, and cooled if needed, at a temperature ofless than 70° C., e.g., less than 50° C., or less than 40° C., anddirectly fed to first column 115.

In one embodiment, the contents of liquid stream 113 are substantiallysimilar to the crude ethanol stream obtained from the reactor, exceptthat the composition has been depleted of hydrogen, carbon dioxide,methane and/or ethane, which have been removed by separator 110.Accordingly, liquid stream 113 may also be referred to as a crudeethanol stream. Exemplary components of liquid stream 113 are providedin Table 2. It should be understood that liquid stream 113 may containother components, not listed in Table 2.

TABLE 2 FEED COMPOSITION TO COLUMN 115 (Liquid Stream 113) Conc. (wt. %)Conc. (wt. %) Conc. (wt. %) Ethanol 5 to 72 10 to 70  15 to 65 AceticAcid <90 5 to 80  0 to 35 Water 5 to 40 5 to 30 10 to 26 Ethyl Acetate<30 1 to 25  3 to 20 Acetaldehyde <10 0.001 to 3    0.1 to 3   Acetal <50.01 to 5    0.01 to 3   Acetone <5 0.0005 to 0.05   0.001 to 0.03 

The amounts indicated as less than (<) in the tables throughout thepresent specification are preferably not present and if present may bepresent in amounts greater than 0.0001 wt. %.

In one embodiment, the ethyl acetate concentration in liquid stream 113may affect the first column reboiler duty and size. Decreasing ethylacetate concentrations may allow for reduced reboiler duty and size. Inone embodiment, to reduce the ethyl acetate concentration (a) thecatalyst in reactor 103 may convert ethyl acetate in addition to aceticacid; (b) the catalyst may be less selective for ethyl acetate, and/or(c) the feed to reactor 103, including recycles, may contain less ethylacetate.

In the embodiment shown in FIG. 1, liquid stream 113 is introduced inthe upper part of first column 115, e.g., upper half or upper third. Inaddition to liquid stream 113, an optional extractive agent 116 and anethyl acetate recycle stream 117 are also fed to first column. Dependingon the ethyl acetate concentration of ethyl acetate recycle stream 117,this stream may be introduced above or near the feed point of the liquidstream 113. Depending on the targeted ethyl acetate concentration in thedistillate of first column 115, the feed point of ethyl acetate recyclestream 117 will vary. Due to the relatively high ethanol concentrationsof ethyl acetate recycle stream 117, as shown in Table 6 below, from 70to 90 wt. % ethanol, it is preferred that ethyl acetate recycle stream117 be fed to first column 115 instead of reactor 103.

Liquid stream 113 and ethyl acetate recycle stream 117 collectivelycomprise the organic feed to first column 115. In one embodiment, theorganic feed comprises from 1 to 25% of ethyl acetate recycle stream117, e.g., from 1% to 15% or from 1% to 10%. This amount may varydepending on the production of reactor 103 and amount of ethyl acetateto be recycled.

In some embodiments, there may be optional extractive agent 116 that ispreferably introduced above the liquid stream 113. Optional extractiveagent 116 may be heated from ambient temperature to a temperature of upto 70° C., e.g., up to 50° C., or up to 40° C. In another embodiment,optional extractive agent 116 is not separately preheated, but iswithdrawn from second column 130, and cooled, if necessary, to atemperature of less than 70° C., e.g., less than 50° C., or less than40° C., and directly fed to first column 115. Optional extractive agent116 preferably comprises water that has been retained within the system.As described herein, extractive agent 116 may be obtained from a portionof the second residue. Extractive agent 116 may be a dilute acid streamcomprising up to 20 wt. % acetic acid, e.g., up to 10 wt. % acetic acidor up to 5 wt. % acetic acid. In one embodiment, the mass flow ratio ofwater in extractive agent 116 to the mass flow of the organic feed,which comprises liquid stream 113 and ethyl acetate recycle stream 117,may range from 0.05:1 to 2:1, e.g., from 0.07 to 0.9:1 or from 0.1:1 to0.7:1. It is preferred that the mass flow of extractive agent 116 isless than the mass flow of the organic feed.

In one embodiment, first column 115 is a tray column having from 5 to 90theoretical trays, e.g. from 10 to 60 theoretical trays or from 15 to 50theoretical trays. The number of actual trays for each column may varydepending on the tray efficiency, which is typically from 0.5 to 0.7depending on the type of tray. The trays may be sieve trays, fixed valvetrays, movable valve trays, or any other suitable design known in theart. In other embodiments, a packed column having structured packing orrandom packing may be employed.

When first column 115 is operated under 50 kPa, the temperature of theresidue exiting in line 118 preferably is from 20° C. to 100° C., e.g.,from 30° C. to 90° C. or from 40° C. to 80° C. The base of column 115may be maintained at a relatively low temperature by withdrawing aresidue stream comprising ethanol, ethyl acetate, water, and aceticacid, thereby providing an energy efficiency advantage. The temperatureof the distillate exiting in line 119 from column 115 preferably at 50kPa is from 10° C. to 80° C., e.g., from 20° C. to 70° C. or from 30° C.to 60° C. The pressure of first column 115 may range from 0.1 kPa to 510kPa, e.g., from 1 kPa to 475 kPa or from 1 kPa to 375 kPa. In someembodiments, first column 115 may operate under a vacuum of less than 70kPa, e.g., less than 50 kPa, or less than 20 kPa. Operating under avacuum may decrease the reboiler duty and reflux ratio of first column115. However, a decrease in operating pressure for first column 115 doesnot substantially affect column diameter.

In first column 115, a weight majority of the ethanol, water, aceticacid, are removed from the organic feed, including liquid stream 113 andethyl acetate recycle stream 117, and are withdrawn, preferablycontinuously, as residue in line 118. This includes any water added asan extractive agent 116. Concentrating the ethanol in the residuereduces the amount of ethanol that is recycled to reactor 103 and inturn reduces the size of reactor 103. Preferably less than 10% of theethanol from the organic feed, e.g., less than 5% or less than 1% of theethanol, is returned to reactor 103 from first column 115. In addition,concentrating the ethanol also will concentrate the water and/or aceticacid in the residue. In one embodiment, at least 90% of the ethanol fromthe organic feed is withdrawn in the residue, and more preferably atleast 95%. In addition, ethyl acetate may also be present in the firstresidue in line 118. The reboiler duty may decrease with an ethylacetate concentration increase in the first residue in line 118.

First column 115 also forms a distillate, which is withdrawn in line119, and which may be condensed and refluxed, for example, at a ratiofrom 30:1 to 1:30, e.g., from 10:1 to 1:10 or from 5:1 to 1:5. Highermass flow ratios of water to organic feed may allow first column 115 tooperate with a reduced reflux ratio.

First distillate in line 119 preferably comprises a weight majority ofthe acetaldehyde and ethyl acetate from liquid stream 113, as well asfrom ethyl acetate recycle stream 117. In one embodiment, the firstdistillate in line 119 comprises a concentration of ethyl acetate thatis less than the ethyl acetate concentration for the azeotrope of ethylacetate and water, and more preferably less than 75 wt. %.

In some embodiments, first distillate in stream 119 also comprisesethanol. Returning the first distillate comprising ethanol to thereactor may require an increase in reactor capacity to maintain the samelevel of ethanol efficiency. In one embodiment, it is preferred toreturn to the reactor less than 10% of the ethanol from the crudeethanol stream, e.g., less than 5% or less than 1%. In terms of ranges,the amount of returned ethanol is from 0.01 to 10% of the ethanol in thecrude ethanol stream, e.g. from 0.1 to 5% or from 0.2 to 1%. In oneembodiment, to reduce the amount of ethanol returned, the ethanol may berecovered from the first distillate in line 119. To recover ethanol,first distillate in line 119 is fed, as is shown in FIG. 1, to anoptional extractor 120. Extractor 120 comprises an extraction column 121to recover ethanol and reduce the ethanol concentration recycled toreactor 103. Extraction column 120 may be a multi-stage extractor. Inextraction column 121, the first distillate in line 119 is fed alongwith at least one extractant 122. In one embodiment, extractant 122 maybe selected from the group consisting of benzene, propylene glycol,cyclohexane and mixtures thereof. Although water may be used, extractant122 preferably does not form an azeotrope with ethanol. A suitableextractant 122 is preferably non-carcinogenic and non-hazardous.Preferably, the extractant extracts ethanol from the first distillate inextractant stream 124. The extractant may be recovered from stream 124in recovery column 123 and returned via line 125. The ethanol stream inline 126 may be combined with ethanol product or returned to one of thedistillation columns, such as first column 115. The raffinate 127 may bereturned to reaction zone 101. Preferably, raffinate 127, whichcomprises acetaldehyde and ethyl acetate, is deficient in ethanol withrespect to first distillate in line 119. In one embodiment, raffinatecomprises less than 2 wt. % ethanol, e.g., less than 1 wt. % ethanol orless than 0.5 wt. % ethanol.

Exemplary components of the distillate and residue compositions forfirst column 115 are provided in Table 3 below. It should also beunderstood that the distillate and residue may also contain othercomponents, not listed in Table 3. For convenience, the distillate andresidue of the first column may also be referred to as the “firstdistillate” or “first residue.” The distillates or residues of the othercolumns may also be referred to with similar numeric modifiers (second,third, etc.) in order to distinguish them from one another, but suchmodifiers should not be construed as requiring any particular separationorder.

TABLE 3 LIGHT ENDS COLUMN Conc. (wt. %) Conc. (wt. %) Conc. (wt. %)Distillate Ethyl Acetate  10 to 85 15 to 80 20 to 75 Acetaldehyde 0.1 to70 0.2 to 65  0.5 to 65  Acetal <3 0.01 to 2   0.05 to 1.5  Acetone<0.05 0.001 to 0.03   0.01 to 0.025 Ethanol <25 0.001 to 20   0.01 to15   Water 0.1 to 20  1 to 15  2 to 10 Acetic Acid <2 <0.1 <0.05 ResidueAcetic Acid 0.1 to 50 0.5 to 40   1 to 30 Water   5 to 40  5 to 35 10 to25 Ethanol  10 to 75 15 to 70 20 to 65 Ethyl Acetate 0.005 to 30  0.03to 25   0.08 to 1  

In one embodiment of the present invention, first column 115 may beoperated at a temperature where most of the water, ethanol, and aceticacid are removed into the residue stream and only a small amount ofethanol and water is collected in the distillate stream due to theformation of binary and tertiary azeotropes. The weight ratio of waterin the residue in line 118 to water in the distillate in line 119 may begreater than 1:1, e.g., greater than 2:1. There may be more water inresidue in line 118 when an optional extractive agent 116 is used. Theweight ratio of ethanol in the residue to ethanol in the distillate maybe greater than 1:1, e.g., greater than 2:1.

The amount of acetic acid in the first residue may vary dependingprimarily on the conversion in reactor 103. In one embodiment, when theconversion is high, e.g., greater than 90%, the amount of acetic acid inthe first residue may be less than 10 wt. %, e.g., less than 5 wt. % orless than 2 wt. %. In other embodiments, when the conversion is lower,e.g., less than 90%, the amount of acetic acid in the first residue maybe greater than 10 wt. %.

The first distillate in line 119 preferably is substantially free ofacetic acid, e.g., comprising less than 1000 wppm, less than 500 wppm orless than 100 wppm acetic acid. The distillate may be purged from thesystem or recycled in whole or part to reactor 103. In some embodiments,when the distillate comprises ethyl acetate and acetaldehyde, thedistillate may be further separated, e.g., in a distillation column (notshown), into an acetaldehyde stream and an ethyl acetate stream. Eitherof these streams may be returned to reactor 103 or separated from system100 as additional products. The ethyl acetate stream may also behydrolyzed or reduced with hydrogen, via hydrogenolysis, to produceethanol. When additional ethanol is produced, it is preferred that theadditional ethanol is recovered and not directed to reactor 103.

Some species, such as acetals, may decompose in first column 115 so thatvery low amounts, or even no detectable amounts, of acetals remain inthe distillate or residue.

In addition, an equilibrium reaction between acetic acid/ethanol andethyl acetate may occur in the crude ethanol stream after exitingreactor 103 or first column 115. Without being bound by theory, ethylacetate may be formed in the reboiler of first column 115. Depending onthe concentration of acetic acid in the crude ethanol stream, thisequilibrium may be driven toward formation of ethyl acetate. Thisreaction may be regulated through the residence time and/or temperatureof the crude ethanol stream.

In one embodiment, due to the composition of first residue in line 118,the equilibrium may favor esterification to produce ethyl acetate. Whilethe esterification, either in the liquid or vapor phase, may consumeethanol, the esterification may also reduce the amount of acetic acidthat needs to be removed from the process. Ethyl acetate may be removedfrom first column 115 via esterification between first column 115 andsecond column 130 as shown in FIG. 2. The esterification reactor may beeither a liquid or vapor phase reactor and may comprise an acidiccatalyst. Acid-catalyzed esterification reactions may be used with someembodiments of the present invention. The catalyst should be thermallystable at reaction temperatures. Suitable catalysts may be solid acidcatalysts comprising an ion exchange resin, zeolites, Lewis acid, metaloxides, inorganic salts and hydrates thereof, heteropoly acids, andsalts thereof Silica gel, aluminum oxide, and aluminum phosphate arealso suitable catalysts. Acid catalysts include, but are not limited to,sulfuric acid, and tosic acid. In addition, Lewis acids may also be usedas esterification catalysts, such as scandium(III) or lanthanide(III)triflates, hafnium(IV) or zirconium(IV) salts, and diarylammoniumarenesulfonates. The catalyst may also include sulfonated (sulphonicacid) ion-exchange resins (e.g., gel-type and macroporous sulfonatedstyrene-divinyl benzene IERs), sulfonated polysiloxane resins,sulfonated perfluorinated (e.g., sulfonated poly-perfluoroethylene), orsulfonated zirconia.

To recover ethanol, first residue in line 118 may be further separateddepending on the concentration of acetic acid and/or ethyl acetate. Inmost embodiments of the present invention, residue in line 118 isfurther separated in a second column 130, also referred to as an “acidcolumn.” Second column 130 yields a second residue in line 131comprising acetic acid and water, and a second distillate in line 132comprising ethanol and ethyl acetate. In one embodiment, a weightmajority of the water and/or acetic acid fed to second column 130 isremoved in the second residue in line 131, e.g., at least 60% of thewater and/or acetic acid is removed in the second residue in line 131 ormore preferably at least 80% of the water and/or acetic acid. An acidcolumn may be desirable, for example, when the acetic acid concentrationin the first residue is greater 50 wppm, e.g., greater than 0.1 wt. %,greater than 1 wt. %, e.g., greater than 5 wt. %.

In one embodiment, a portion of the first residue in line 118 may bepreheated prior to being introduced into second column 130, as shown inFIG. 2. The preheating of the first residue in line 118 may be heatintegrated with either the residue of the second column 130 or vaporoverhead of second column 130. At least one portion of first residue inline 118 may pass through either a secondary reactor 160, which ispreferably a vapor phase esterification reactor, or into a secondaryvaporizer 161. Secondary reactor 160 may comprise both a vaporizer and avapor phase esterification reactor that produces a stream in which atleast a portion of the contents are in the vapor phase. Secondaryvaporizer 161 also produces a stream in which at least a portion of thecontents are in the vapor phase. The streams from secondary reactor 160and secondary vaporizer 161 may be combined with a portion of the firstresidue that bypasses the preheating in line 162. The partial vapor feedin line 163 preferred has less than 30 mol. % of the contents in thevapor phase, e.g., less than 25 mol. % or less than 20 mol. %. In termsof ranges, from 1 to 30 mol. % is in the vapor phase, e.g., from 5 to 20mol. %. Greater vapor phase contents result in increased energyconsumption and a significant increase in the size of second column 130.It should be understood that the preheating of FIG. 2 may be combinedwith the features shown in FIG. 1.

Esterifying the acetic acid in first residue in line 118 increases theethyl acetate concentration which leads to increases in the size ofsecond column 130 as well increases in reboiler duty. Thus, theconversion of acetic acid may be controlled depending on the initialethyl acetate concentration withdrawn from first column. To maintain anefficient separation the ethyl acetate concentration of the firstresidue in line 118 feed to second column is preferably less than 1000wppm, e.g., less than 800 wppm or less than 600 wppm.

Second column 130 operates in a manner to concentrate the ethanol fromfirst residue so that a majority of the ethanol is carried overhead.Thus, the residue of second column 130 may have a low ethanolconcentration of less than 5 wt. %, e.g. less than 1 wt. % or less than0.5 wt. %. Lower ethanol concentrations may be achieved withoutsignificant increases in reboiler duty or column size. Thus, in someembodiments, it is efficient to reduce the ethanol concentration in theresidue to less than 50 wppm, or more preferably less than 25 wppm. Asdescribed herein, the residue of second column 130 may be treated andlower concentrations of ethanol allow the residue to be treated withoutgenerating further impurities.

In FIG. 1, the first residue in line 118 is introduced to second column130 preferably in the top part of column 130, e.g., top half or topthird. Feeding first residue in line 118 in a lower portion of secondcolumn 130 may unnecessarily increase the energy requirements of secondcolumn 130. Acid column 130 may be a tray column or packed column. InFIG. 1, second column 130 may be a tray column having from 10 to 110theoretical trays, e.g. from 15 to 95 theoretical trays or from 20 to 75theoretical trays. Additional trays may be used if necessary to furtherreduce the ethanol concentration in the residue. In one embodiment, thereboiler duty and column size may be reduced by increasing the number oftrays.

Although the temperature and pressure of second column 130 may vary,when at atmospheric pressure the temperature of the second residue inline 131 preferably is from 95° C. to 160° C., e.g., from 100° C. to150° C. or from 110° C. to 145° C. In one embodiment, first residue inline 118 is preheated to a temperature that is within 20° C. of thetemperature of second residue in line 131, e.g., within 15° C. or within10° C. The temperature of the second distillate exiting in line 132 fromsecond column 130 preferably is from 50° C. to 120° C., e.g., from 75°C. to 118° C. or from 80° C. to 115° C. The temperature gradient may besharper in the base of second column 130.

The pressure of second column 130 may range from 0.1 kPa to 510 kPa,e.g., from 1 kPa to 475 kPa or from 1 kPa to 375 kPa. In one embodiment,second column 130 operates above atmospheric pressure, e.g., above 170kPa or above 375 kPa. Second column 130 may be constructed of a materialsuch as 316L SS, Allot 2205 or Hastelloy C, depending on the operatingpressure. The reboiler duty and column size for second column 130 remainrelatively constant until the ethanol concentration in the seconddistillate in line 132 is greater than 90 wt. %.

In one optional embodiment, first column 115 is an extractive columnthat preferably uses water. The additional water is separated in secondcolumn 130. While using water as an extractive agent may reduce thereboiler duty of first column 115, when the mass flow ratio of water toorganic feed is larger than 0.65:1, e.g., larger than 0.6:1 or largerthan 0.54:1, the additional water will cause an increase in reboilerduty of second column 130 that offsets any benefit gained by firstcolumn 115.

Second column 130 also forms an overhead, which is withdrawn in line133, and which may be condensed and refluxed, for example, at a ratiofrom 12:1 to 1:12, e.g., from 10:1 to 1:10 or from 8:1 to 1:8. Theoverhead in line 133 preferably comprises 85 to 92 wt. % ethanol, e.g.,about 87 to 90 wt. % ethanol, with the remaining balance being water andethyl acetate.

In one embodiment, water may be removed prior to recovering the ethanolproduct. In one embodiment, the overhead in line 133 may comprise lessthan 15 wt. % water, e.g., less than 10 wt. % water or less than 8 wt. %water. As shown in FIG. 1, overhead vapor in line 133 may be fed towater separator 135, which may be an adsorption unit, membrane,molecular sieves, extractive column distillation, or a combinationthereof. In one embodiment, at least 50% of overhead vapor is fed towater separator 135, e.g., at least 75% or at least 90%. Optionally,some of overhead vapor in line 133 is condensed as second distillate 132and optionally may be fed directly to third distillation column 140.

Water separator 135 in FIG. 1 may be a pressure swing adsorption (PSA)unit. For purposes of clarity, the details of the PSA unit are not shownin the figures. The PSA unit is optionally operated at a temperaturefrom 30° C. to 160° C., e.g., from 80° C. to 140° C., and a pressurefrom 0.01 kPa to 550 kPa, e.g., from 1 kPa to 150 kPa. The PSA unit maycomprise two to five beds. Water separator 135 may remove at least 95%of the water overhead vapor 133, and more preferably from 95% to 99.99%of the water from vapor overhead 133, into a water stream 134. All or aportion of water stream 134 may be returned to second column 130 in line136, which may increase the reboiler duty and/or size of second column130. Additionally or alternatively, all or a portion of water stream maybe purged via line 137. The remaining portion of vapor overhead 133exits the water separator 135 as ethanol mixture stream 138. In oneembodiment, ethanol mixture stream 138 comprises more than 92 wt. %ethanol, e.g., more than 95 wt. % or more than 99 wt. %. In oneembodiment a portion of water stream 137 may be fed to first column 115as the extractive agent (not shown).

A portion of vapor overhead 133 may be condensed and refluxed to secondcolumn 130, as shown, for example, at a ratio from 12:1 to 1:12, e.g.,from 10:1 to 1:10 or from 8:1 to 1:8. The second distillate in line 132optionally may be mixed with ethanol mixture stream 138 and co-fed toproduct column 140. This may be necessary if additional water is neededto improve separation in product column 140. It is understood thatreflux ratios may vary with the number of stages, feed locations, columnefficiency and/or feed composition. Operating with a reflux ratio ofgreater than 3:1 may be less preferred because more energy may berequired to operate second column 130.

Exemplary components for ethanol mixture stream 138 and residuecompositions for second column 130 are provided in Table 4 below. Itshould be understood that the distillate and residue may also containother components, not listed in Table 4. For example, in optionalembodiments, when ethyl acetate is in the feed to reactor 103, secondresidue in line 131 exemplified in Table 4 may also comprise highboiling point components.

TABLE 4 ACID COLUMN Conc. (wt. %) Conc. (wt. %) Conc. (wt. %) EthanolMixture Stream Ethanol  90 to 99.9    92 to 99    96 to 99 Ethyl Acetate<10 0.001 to 5 0.005 to 4 Acetaldehyde <10 0.001 to 5 0.005 to 4 Water<10 0.001 to 3  0.01 to 1 Acetal <2 0.001 to 1   0.005 to 0.5 SecondResidue Acetic Acid 0.1 to 45     0.2 to 40   0.5 to 35 Water 45 to 100    55 to 99.8     65 to 99.5 Ethyl Acetate <0.1   0.0001 to 0.05  0.0001 to 0.01 Ethanol <5 0.002 to 1   0.005 to 0.5

The weight ratio of ethanol in ethanol mixture stream 138 to ethanol inthe second residue in line 131 preferably is at least 35:1. Preferably,ethanol mixture stream 138 is substantially free of acetic acid and maycontain, if any, trace amounts of acetic acid.

In one embodiment, ethyl acetate fed to second column 130 mayconcentrate in the vapor overhead and pass through with ethanol mixturestream 138. Thus, preferably no ethyl acetate is withdrawn in the secondresidue in line 131. Advantageously this allows most of the ethylacetate to be subsequently recovered without having to further processthe second residue in line 131.

In optional embodiments, the feed to reactor 103 may comprise aceticacid and/or ethyl acetate. When ethyl acetate is used alone as a feed,the crude ethanol stream may comprise substantially no water and/oracetic acid. There may be high boiling point components, such asalcohols having more than 2 carbon atoms, e.g., n-propanol, isopropanol,n-butanol, 2-butanol, and mixtures thereof High boiling point componentsrefer to compounds having a boiling point that is greater than ethanol.The high boiling point components may be removed in second column 130 inthe second residue in line 131 described herein.

As discussed above, according to the present invention, unreacted aceticacid in the second residue in line 131 (also referred to as the diluteacid stream) is directed to esterification unit 120. In someembodiments, the second residue in line 131 may comprise at least 85% ofthe acetic acid from crude ethanol stream 109, e.g., at least 90% andmore preferably at least 99%. In terms of ranges, the dilute acid streamoptionally comprises from 85% to 99.5% or from 90% to 99.99% of theunreacted acetic acid from the crude ethanol stream. In one embodiment,substantially all of the unreacted acetic acid is recovered in thesecond residue in line 131. By removing substantially all of theunreacted acetic acid from crude ethanol stream 109, the process, insome aspects, advantageously does not require further separation ofacetic acid from the ethanol. In some embodiments, the dilute acidstream comprises from 0.1 to 55 wt. % acetic acid and from 45 to about99 wt. % water.

In one embodiment, substantially all of the unreacted acetic acid isreacted out of second residue in line 131. According to FIG. 1, secondresidue in line 131 is co-fed to esterification unit 150 with alcoholstream 151 to produce an ester product stream 152 comprising one or moreesters and bottoms 153 comprising water. In one embodiment, esterproduct stream 152 and/or bottoms 153 may be substantially free ofacetic acid. Second residue in line 131 may be fed to esterificationunit 150 at a temperature from 20 to 90° C., e.g., from 25 to 75° C.Preheating may be used as necessary. In some embodiments, alcohol stream151 and second residue in line 131 are fed to the esterification unit ina counter-current manner to facilitate the production of a reactionproduct. In another embodiment, not shown, alcohol stream 151 may beadded directly to second residue in line 131 prior to being introducedinto esterification unit 150. The alcohol in alcohol stream 151 may beany suitable alcohol, such as methanol, ethanol, propanol, butanol, ormixtures thereof Preferably, the alcohol is methanol.

In some embodiments, esterification unit 150 comprises a reaction zonecomprising a reactor, coupled to a separation zone comprising one ormore distillation columns and/or stripping columns. Suitable reactorsfor use in the esterification include batch reactors, continuously-fedstirred-tank reactors, plug-flow reactors, reactive distillation towers,or a combination thereof. In some embodiments, an acid catalyst is fedto the reactor to facilitate the esterification of the acetic acid.Suitable acid catalysts for use in the present invention include, butare not limited to sulfuric acid, phosphoric acid, sulfonic acids,heteropolyacids, other mineral acids and a combination thereof.

The residence time of esterification unit 150 may impact acetic acidconversion. In some embodiments, for example, the residence time inesterification unit 150 is from 0.1 to 5 hours, e.g., from 0.2 to 3hours, or less than 1 hour.

The distillation column for the esterification unit 150 may comprisefrom 5 to 70 theoretical trays, e.g., from 10 to 50 theoretical trays orfrom 15 to 30 theoretical trays. The reflux of ester product stream 152may be from 10:1 to 1:10, e.g., from 5:1 to 1:5 or from 2:1 to 1:2.

The operating parameters of esterification unit 150 may be varied toachieve a desired composition in ester product stream 152. For example,in some embodiments, temperature, pressure, feed rates, and residencetimes can be varied to increase conversion of acetic acid to an ester,decrease the formation of impurities, achieve more efficient separation,reduce energy consumption, or combinations thereof.

In one embodiment, esterification unit 150 operates at a basetemperature from 100° C. to 150° C., e.g., from 100° C. to 130° C., orfrom 100° C. to 120° C. In terms of pressure, esterification unit 120may be operated at atmospheric pressure, subatmospheric pressure, orsuperatmospheric pressure. For example, in some embodiments,esterification unit 150 operates at a pressure from 50 kPa to 500 kPa,e.g., from 50 kPa to 400 kPa, or from 50 kPa to 200 kPa.

In some embodiments, the feed rates of acetic acid and alcohol to theesterification unit 150 may be adjusted to control the molar ratio ofacetic acid to alcohol being fed to the esterification unit 150. Forexample, in some embodiments, the molar ratio of acetic acid to methanolfed to the esterification unit 150 is from 1:1 to 1:50, e.g., from 1:2to 1:35, or from 1:5 to 1:20.

The processes of the present invention preferably provide for a highconversion of acetic acid to ester(s). In one embodiment, at least 60%,e.g., at least 75%, at least 90% or at least 95% of the acetic acid inthe second residue in line 131 is converted to an ester. Lowerconversion of acetic acid may be tolerated if the acetic acidconcentration in second residue in line 132 is relatively low.

The ester product stream 152 exiting the esterification unit 150preferably comprises at least one ester. Exemplary compositions whenusing methanol as the alcohol stream 151 from the esterification unit150 are provided in Table 5, below. It should also be understood thatthese compositions may also contain other components, not listed inTable 5. Lower amounts of the ester may be possible when higherconcentrations of the alcohols are fed to the reactor relative to theacetic acid to be reacted. When excess alcohol is reacted with theacetic acid from the second residue in line 131, some alcohol also maybe present in the ester product stream 152.

TABLE 5 ESTERIFICATION UNIT 150 Conc. (wt. %) Conc. (wt. %) Conc. (wt.%) Ester Product Stream Methyl Acetate 1 to 90    5 to 85    to 90Methanol 40 to 99.9  45 to 95  50 to 90 Water <1 0.001 to 0.5 0.001 to0.1 Acetic Acid <0.1 <0.5  nd Ether <1 0.001 to 0.5 0.001 to 0.1 BottomsWater 90 to 99.9    92 to 99.9    95 to 99.9 Acetic Acid <5 0.001 to 3  0.01 to 1  Methanol <1 <0.001 nd Methyl Acetate <1 <0.05   0.0001 to0.005

Some impurities, such as dimethyl ether may form over the course of thereaction in esterification unit 150. These impurities may be present invery low amounts, or even no detectable amounts, in the ester productstream 152. In some embodiments, the ester product stream 152 comprisesless than 1000 wppm dimethyl ether, e.g., less than 750 wppm, or lessthan 500 wppm.

In some embodiments, esterification unit 150 comprises a reactivedistillation column. Reactive distillation column comprises an ionexchange resin bed, an acidic catalyst, or combinations thereofNon-limiting examples of ion exchange resins suitable for use in thepresent invention include macroporous strong-acid cation exchange resinssuch as those from the Amberlyst® series distributed by Rohm and Haas.Additional ion exchange resins suitable for use in the present inventionare disclosed in U.S. Pat. Nos. 4,615,806, 5,139,981, and 7,588,690, thedisclosures of which are incorporated by reference in their entireties.In other embodiments, reactive distillation column comprises an acidselected from the group consisting of sulfuric acid, phosphoric acid,sulfonic acids, heteropolyacids, other mineral acids and a combinationthereof. In other embodiments, acid catalysts include zeolites andsupports treated with mineral acids and heteropolyacids. When an acidcatalyst is used, e.g., sulfuric acid, the acid catalyst is fed to thereactive distillation column.

In some embodiments, second residue in line 131 is optionally fed to aguard bed (not shown) and then fed to esterification unit 150. In thisaspect, the guard bed comprises an ion exchange resin, such as thosedisclosed above. While not being bound to any particular theory, theguard bed removes one or more corrosive metals present in the secondresidue in line 131, thereby minimizing the deactivation of any ionexchange resin catalytic sites in the ion exchange resin present inesterification unit 150.

Bottoms 153 comprising water and may be substantially free of aceticacid. In one embodiment, a portion of bottoms 153 in optional line 154may be directed to first column 115 as an optional extractive agent. Inother embodiments, bottoms 153 may be used to hydrolize a streamcomprising ethyl acetate or diethyl acetal. Bottoms 153 may also beneutralized and/or diluted before being disposed of to a waste watertreatment facility. The organic content, e.g., acetic acid content, ofbottoms 153 beneficially may be suitable to feed microorganisms used ina waste water treatment facility.

As described above, ester product stream 152 may be further processedand/or refined. In one embodiment, a portion of ester product stream 152is fed to a carbonylation process along with carbon monoxide to produceacetic acid. Suitable carbonylation processes are described above. Thisallows an indirect recycle of the unreacted acetic acid in thehydrogenation process through the carbonylation process and back to thehydrogenation process.

In an optional embodiment, ester product stream 152 may be reduced withhydrogen to form ethanol via hydrogenolysis. The resulting ethanol maybe removed as a separate product or recycled to the process, such as tofirst column 115, second column 130, or esterification unit 150.

In one embodiment, due to the presence of ethyl acetate in ethanolmixture stream 138, an additional third column 140 may be used. A thirdcolumn 140, referred to as a “light ends” column, is used for removingethyl acetate from ethanol mixture stream 138 and producing an ethanolproduct in the third residue in line 141. Product column 140 may be atray column or packed column. In FIG. 1, third column 140 may be a traycolumn having from 5 to 90 theoretical trays, e.g. from 10 to 60theoretical trays or from 15 to 50 theoretical trays.

The feed location of ethanol mixture stream 138 may vary depending onethyl acetate concentration and it is preferred to feed ethanol mixturestream 138 to the upper portion of third column 140. Higherconcentrations of ethyl acetate may be fed at a higher location in thirdcolumn 140. The feed location should avoid the very top trays, near thereflux, to avoid excess reboiler duty requirements for the column and anincrease in column size. For example, in a column having 45 actualtrays, the feed location should be between 10 to 15 trays from the top.Feeding at a point above this may increase the reboiler duty and size ofproduct column 140.

Ethanol mixture stream 138 may be fed to third column 140 at atemperature of up to 70° C., e.g., up to 50° C., or up to 40° C. In someembodiments it is not necessary to further preheat ethanol mixturestream 138.

Ethyl acetate may be concentrated in the third distillate in line 142.Due to the relatively lower amounts of ethyl acetate fed to third column140, third distillate in line 142 also comprises substantial amounts ofethanol. To recover the ethanol, third distillate in line 142 may be fedto first column as the ethyl acetate recycle stream 117. Because thisincreases the demands on the first and second columns, it is preferredthat the concentration of ethanol in third distillate in line 142 befrom 70 to 90 wt. %, e.g., from 72 to 88 wt. %, or from 75 to 85 wt. %.

In other embodiments, a portion of third distillate in line 142 may bepurged from the system in line 143 as a separate product, such as anethyl acetate solvent.

In some embodiments to recover the ethanol without sending thirddistillate in line 142 back to first column 115, the ethanol may berecovered using an extractive column 145 as shown in FIG. 4. In otherembodiments, a portion of third distillate in line 142 may be purgedfrom the system in line 143 as a separate product, such as an ethylacetate solvent. In addition, ethanol may be recovered from a portion ofthe third distillate in line 142 using an extractant, such as benzene,propylene glycol, and cyclohexane, such that the raffinate comprisesless ethanol to recycle.

In an optional embodiment, the third residue may be further processed torecover ethanol with a desired amount of water, for example, using afurther distillation column, adsorption unit, membrane or combinationthereof, may be used to further remove water from third residue in line141 as necessary. In most embodiments, the water is removed prior tothird column 140 using water separator 135 and thus further drying ofthe ethanol is not required.

Third column 140 is preferably a tray column as described above andpreferably operates at atmospheric pressure. The temperature of thethird residue in line 141 exiting from third column 140 preferably isfrom 65° C. to 110° C., e.g., from 70° C. to 100° C. or from 75° C. to80° C. The temperature of the third distillate in line 142 exiting fromthird column 140 preferably is from 30° C. to 70° C., e.g., from 40° C.to 65° C. or from 50° C. to 65° C.

The pressure of third column 140 may range from 0.1 kPa to 510 kPa,e.g., from 1 kPa to 475 kPa or from 1 kPa to 375 kPa. In someembodiments, third column 140 may operate under a vacuum of less than 70kPa, e.g., less than 50 kPa, or less than 20 kPa. Decreases in operatingpressure substantially decrease column diameter and reboiler duty forthird column 140.

Exemplary components for ethanol mixture stream and residue compositionsfor third column 140 are provided in Table 6 below. It should beunderstood that the distillate and residue may also contain othercomponents, not listed in Table 6.

TABLE 6 PRODUCT COLUMN Conc. (wt. %) Conc. (wt. %) Conc. (wt. %) ThirdDistillate Ethanol 70 to 99    72 to 90 75 to 85 Ethyl Acetate 0.5 to30     1 to 25  1 to 15 Acetaldehyde <15  0.001 to 10 0.1 to 5   Water<10 0.001 to 2 0.01 to 1   Acetal <2 0.001 to 1 0.01 to 0.5  ThirdResidue Ethanol   80 to 99.5    85 to 97 90 to 95 Water <8 0.001 to 30.01 to 1   Ethyl Acetate <1.5 0.0001 to 1  0.001 to 0.5  Acetic Acid<0.5 <0.01 0.0001 to 0.01 

When first residue in line 118 comprise low amounts of acetic acidand/or there is no esterification of first residue, such that the ethylacetate concentration is less than 50 wppm, third column 140 may beoptional. Thus, ethanol mixture stream 138 from the water separator 135may be the ethanol product and there is no ethyl acetate recycle stream.

Depending on the amount of water and acetic acid contained in the secondresidue in line 131 may be treated in one or more of the followingprocesses. One process involving an esterification unit 150 is shown inFIG. 1. A suitable weak acid recovery system is described in US Pub. No.2012/0010446, the entire contents and disclosure of which is herebyincorporated by reference. When the residue comprises a majority ofacetic acid, e.g., greater than 70 wt. %, the residue may be recycled tothe reactor without any separation of the water. In one embodiment, theresidue may be separated into an acetic acid stream and a water streamwhen the residue comprises a majority of acetic acid, e.g., greater than50 wt. %. Acetic acid may also be recovered in some embodiments fromfirst residue having a lower acetic acid concentration. The residue maybe separated into the acetic acid and water streams by a distillationcolumn or one or more membranes. If a membrane or an array of membranesis employed to separate the acetic acid from the water, the membrane orarray of membranes may be selected from any suitable acid resistantmembrane that is capable of removing a permeate water stream. Theresulting acetic acid stream optionally is returned to reactor 103. Theresulting water stream may be used as an extractive agent or tohydrolyze an ester-containing stream in a hydrolysis unit.

In other embodiments, for example where second residue in line 131comprises less than 50 wt. % acetic acid, possible options include oneor more of: (i) returning a portion of the residue to reactor 103, (ii)neutralizing the acetic acid, (iii) reacting the acetic acid with analcohol, or (iv) disposing of the residue in a waste water treatmentfacility. It also may be possible to separate a residue comprising lessthan 50 wt. % acetic acid using a weak acid recovery distillation columnto which a solvent (optionally acting as an azeotroping agent) may beadded. Exemplary solvents that may be suitable for this purpose includeethyl acetate, propyl acetate, isopropyl acetate, butyl acetate, vinylacetate, diisopropyl ether, carbon disulfide, tetrahydrofuran,isopropanol, ethanol, and C₃-C₁₂ alkanes. When neutralizing the aceticacid, it is preferred that the residue in line 131 comprises less than10 wt. % acetic acid. Acetic acid may be neutralized with any suitablealkali or alkaline earth metal base, such as sodium hydroxide orpotassium hydroxide. When reacting acetic acid with an alcohol, it ispreferred that the residue comprises less than 50 wt. % acetic acid. Thealcohol may be any suitable alcohol, such as methanol, ethanol,propanol, butanol, or mixtures thereof. The reaction forms an ester thatmay be integrated with other systems, such as carbonylation productionor an ester production process. Preferably, the alcohol comprisesethanol and the resulting ester comprises ethyl acetate. Optionally, theresulting ester may be fed to the hydrogenation reactor.

In some embodiments, when the residue in line 131 comprises very minoramounts of acetic acid, e.g., less than 5 wt. % or less than 1 wt. %,the residue may be neutralized and/or diluted before being disposed ofto a waste water treatment facility. The organic content, e.g., aceticacid content, of the residue beneficially may be suitable to feedmicroorganisms used in a waste water treatment facility.

The associated condensers and liquid separation vessels that may beemployed with each of the distillation columns may be of anyconventional design and are simplified in the figures. Heat may besupplied to the base of each column or to a circulating bottom streamthrough a heat exchanger or reboiler. Other types of reboilers, such asinternal reboilers, may also be used. The heat that is provided to thereboilers may be derived from any heat generated during the process thatis integrated with the reboilers or from an external source such asanother heat generating chemical process or a boiler. Although onereactor and one flasher are shown in the figures, additional reactors,flashers, condensers, heating elements, and other components may be usedin various embodiments of the present invention. As will be recognizedby those skilled in the art, various condensers, pumps, compressors,reboilers, drums, valves, connectors, separation vessels, etc., normallyemployed in carrying out chemical processes may also be combined andemployed in the processes of the present invention.

The temperatures and pressures employed in the columns may vary.Temperatures within the various zones will normally range between theboiling points of the composition removed as the distillate and thecomposition removed as the residue. As will be recognized by thoseskilled in the art, the temperature at a given location in an operatingdistillation column is dependent on the composition of the material atthat location and the pressure of column. In addition, feed rates mayvary depending on the size of the production process and, if described,may be generically referred to in terms of feed weight ratios.

The ethanol product produced by the process of the present invention maybe an industrial grade ethanol or fuel grade ethanol. Exemplary finishedethanol compositional ranges are provided below in Table 7.

TABLE 7 FINISHED ETHANOL COMPOSITIONS Component Conc. (wt. %) Conc. (wt.%) Conc. (wt. %) Ethanol 85 to 99.9 90 to 99.5 92 to 99.5 Water <8 0.1to 3    0.1 to 1    Acetic Acid <1 <0.1 <0.01 Ethyl Acetate <2 <0.5<0.05 Acetal <0.05 <0.01 <0.005 Acetone <0.05 <0.01 <0.005 Isopropanol<0.5 <0.1 <0.05 n-propanol <0.5 <0.1 <0.05

The finished ethanol composition of the present invention preferablycontains very low amounts, e.g., less than 0.5 wt. %, of other alcohols,such as methanol, butanol, isobutanol, isoamyl alcohol and other C₄-C₂₀alcohols. In one embodiment, the amount of isopropanol in the finishedethanol composition is from 80 to 1,000 wppm, e.g., from 95 to 1,000wppm, from 100 to 700 wppm, or from 150 to 500 wppm. In one embodiment,the finished ethanol composition is substantially free of acetaldehyde,optionally comprising less than 8 wppm acetaldehyde, e.g., less than 5wppm or less than 1 wppm.

The finished ethanol composition produced by the embodiments of thepresent invention may be used in a variety of applications includingapplications as fuels, solvents, chemical feedstocks, pharmaceuticalproducts, cleansers, sanitizers, hydrogen transport or consumption. Infuel applications, the finished ethanol composition may be blended withgasoline for motor vehicles such as automobiles, boats and small pistonengine aircraft. In non-fuel applications, the finished ethanolcomposition may be used as a solvent for toiletry and cosmeticpreparations, detergents, disinfectants, coatings, inks, andpharmaceuticals. The finished ethanol composition may also be used as aprocessing solvent in manufacturing processes for medicinal products,food preparations, dyes, photochemicals and latex processing.

The finished ethanol composition may also be used as a chemicalfeedstock to make other chemicals such as vinegar, ethyl acrylate, ethylacetate, ethylene, glycol ethers, ethylamines, aldehydes, and higheralcohols, especially butanol. In the production of ethyl acetate, thefinished ethanol composition may be esterified with acetic acid. Inanother application, the finished ethanol composition may be dehydratedto produce ethylene.

While the invention has been described in detail, modifications withinthe spirit and scope of the invention will be readily apparent to thoseof skill in the art. In addition, it should be understood that aspectsof the invention and portions of various embodiments and variousfeatures recited herein and/or in the appended claims may be combined orinterchanged either in whole or in part. In the foregoing descriptionsof the various embodiments, those embodiments which refer to anotherembodiment may be appropriately combined with one or more otherembodiments, as will be appreciated by one of skill in the art.Furthermore, those of ordinary skill in the art will appreciate that theforegoing description is by way of example only, and is not intended tolimit the invention.

We claim:
 1. A process for producing ethanol comprising: hydrogenatingacetic acid and/or an ester thereof in a reactor in the presence of acatalyst to form a crude ethanol stream; separating a portion of thecrude ethanol stream in a first distillation column to yield a firstdistillate comprising acetaldehyde, ethyl acetate and ethanol, and afirst residue comprising ethanol, acetic acid and ethyl acetate;separating a portion of the first residue in a second distillationcolumn to yield a second residue comprising acetic acid and a seconddistillate comprising ethanol and ethyl acetate; and separating at leasta portion of the second distillate in a third distillation column toyield a third distillate comprising ethyl acetate and a third residuecomprising ethanol, wherein the first distillate is returned to thereactor and less than 10% of the ethanol from the crude ethanol streamis returned to the reactor.
 2. The process of claim 1, wherein less than5% of the ethanol from the crude ethanol stream is returned to thereactor.
 3. The process of claim 1, wherein from 0.1 to 10% of theethanol from the crude ethanol stream is returned to the reactor.
 4. Theprocess of claim 1, wherein at least 90% of the ethanol in the crudeethanol stream is withdrawn into the first residue.
 5. The process ofclaim 1, wherein the third distillate comprises from 70 to 99 wt. %ethanol.
 6. The process of claim 1, wherein the third distillate isintroduced to the first column.
 7. The process of claim 1, wherein thefirst distillate is further separated to yield an ethanol stream and araffinate stream comprising ethyl acetate.
 8. The process of claim 7,wherein the raffinate stream comprises less than 2 wt. % ethanol.
 9. Theprocess of claim 7, wherein at least a portion of the raffinate streamis returned to the reactor.
 10. The process of claim 7, wherein at leasta portion of the ethanol stream is combined with the third residue. 11.The process of claim 7, wherein at least a portion of the ethanol streamis fed to the third distillation column.
 12. The process of claim 1,wherein the ethanol has a ¹⁴C:¹²C ratio of the acetic acid from 0.5 to 1of the ¹⁴C:¹²C ratio for living organisms.
 13. The process of claim 1,wherein a total diameter for the first distillation column, the seconddistillation column and the third distillation column is from 5 to 40meters and further wherein a ratio of total column diameter for thefirst distillation column, the second distillation column and the thirddistillation column to tons of ethanol produced per hour is from 1:2 to1:30.
 14. A process for producing ethanol comprising: hydrogenatingacetic acid and/or an ester thereof in a reactor in the presence of acatalyst to form a crude ethanol stream; separating a portion of thecrude ethanol stream in a first distillation column to yield a firstdistillate comprising acetaldehyde and ethyl acetate, and a firstresidue comprising ethanol, acetic acid and water; converting a portionof the first residue into a partial vapor feed having less than 30 mol.% of the contents in the vapor phase; separating a portion of thepartial vapor feed in a second distillation column to yield a secondresidue comprising acetic acid and a second distillate comprisingethanol; and recovering ethanol from the second distillate.
 15. Theprocess of claim 14, wherein a portion of the first residue is fed to asecondary reactor to convert at least some of the contents into thevapor phase.
 16. The process of claim 15, wherein the secondary reactoris a vapor phase esterification reactor.
 17. The process of claim 14,wherein a portion of the first residue is fed to a secondary vaporizerto convert at least some of the contents into the vapor phase.
 18. Theprocess of claim 14, wherein the partial vapor feed has less has than 25mol. % of the contents in the vapor phase.
 19. The process of claim 14,wherein the partial vapor feed has from 0.1 to 30 mol. % of the contentsin the vapor phase.
 20. The process of claim 14, further comprisingremoving water from at least a portion of the second distillate using anadsorption unit, membrane, extractive column distillation, molecularsieve, or a combination thereof to yield an ethanol product streamhaving a lower water content than the at least a portion of the seconddistillate.
 21. The process of claim 14, further comprising separatingat least a portion of the second distillate in a third distillationcolumn to yield a third distillate comprising ethyl acetate and a thirdresidue comprising ethanol.
 22. The process of claim 14, wherein thefirst distillate further comprises ethanol, the first distillate isreturned to the reactor, and wherein less than 10% of the ethanol fromthe crude ethanol stream is returned to the reactor.